1. Field of the Disclosure
The present invention relates to a nitrogen-doped carbon electrocatalyst, a fuel cell and a metal-air battery containing the electrocatalyst, and a method for making the electrocatalyst.
2. Description of Related Art
In recent years, the development of nitrogen-doped carbon electrocatalysts has gained attention of researchers in the fuel cell and air battery fields owing to the problems relating to the use of Pt-based materials. The slow kinetics of oxygen reduction reaction (ORR), high cost, and low stability of Pt-catalysts had been the most important factors impeding the mass commercialization of fuel cells (Adina M., Pascale J, Bruno J, and Serge P., Phys. Chem. Chem. Phys., 2011, 13, 21600-21607; R. Bashyam and P. Zelenay, Nature, 2006, 442, 63-66—each incorporated by reference in its entirety). Nitrogen-doped carbon, however, had been recognized as a potential Pt-free catalyst for fuel cells (Hali P, Changting H, Jinhua C, Bo L, Yafei K, Xiaohua Z, (2010) J. Solid State Electrochem 14:169; Liang H C, chen F, Li R G, Wang L, Deng Z H (2004) Electrochim Acta 49:3463—each incorporated by reference in its entirety).
Investigators have employed ammonium peroxydisulfate {(NH4)2S2O8, APS} for the stoichiometric polymerization of aniline (PANI) on a carbon support as a potential fuel cell electrocatalyst. G. Wu et al. (2011) used APS for polymerization of liquid aniline with ketjenblack carbon (KB) and obtained good ORR activity. Also, Lei Fu et al. (2010) developed activated carbon/polyaniline (PANI) with a good ORR activity by using the same APS as a main oxidant for polymerization of liquid aniline. Furthermore, APS oxidant was also employed by B. Merzougui et al. (2013) to deposit PANI from liquid aniline on multi-walled carbon nanotubes.
In an effort to avoid the use of APS as oxidant, Zelenay et al. (2010) of Los Alamos Laboratory came up with a simple synthesis method of sulfur-free approach by employing FeCl3 as an oxidant for polymerizing liquid aniline to obtain a cathode catalyst. APS is known to be a good oxidant, but its side reaction products are sometimes difficult to remove. It has been noticed that formation of sulfur containing compounds, such as FeS which are known to be poison towards oxygen reduction reaction, could occur. Using APS requires several washings of the produced catalyst and sometimes acid treatment, which in most cases requires a second heat treatment, which is a complicated time consuming step.